The field of the invention is wheel bearings and the invention relates more particularly to wheel bearings of the type used in shopping cart wheels.
Shopping cart wheels are expected to carry larger and larger loads with the proliferation of large super stores. It is not uncommon for a shopping cart to be loaded with many cases of paper or canned goods which can increase the load to several hundred pounds. Shopping cart wheels of a generation ago would not be capable of withstanding such loads. Shopping cart wheels also must be able to be fabricated economically since they are used in very large quantities. Furthermore, high pressure detergent washing is often used to cleanse shopping carts and these can remove lubricants from wheel bearings and lead to noisy or poorly turning wheels.
While many wheel bearings are designed to eliminate as much friction as possible, it is actually advantageous to have a slight amount of friction in a shopping cart wheel. This is because shopping carts are often left on a slightly sloped parking lot, both while they are being unloaded and when they are empty. If the wheel bearings were set to almost completely eliminate friction, these carts would be almost impossible to keep motionless, if the surface was not absolutely horizontal. Thus, friction adding means are often provided with shopping cart wheel bearing assemblies.